“Communities will be forced to respond in one way or another to the increased erosion and coastal storm damage,” economists at San Francisco State University concluded in a recent study. Communities can either plan for the long term or improvise, storm by storm, until ad hoc solutions are inadequate, they warned.

Officials in cities across the United States and Canada are staying in close touch with San Francisco planners. “People often wait to see what California does” about environmental hazards, said Gary B. Griggs, a professor of earth and planetary sciences at the University of California, Santa Cruz. “So we have a chance to have a big impact.”